Hot Rods Big Block Chevy header gaskets

I have a BBC with LS6 iron heads and ****** Super Comp 2.125" headers. Not getting a good seal with the current copper round port header gaskets. I have a set of square port embossed gaskets which will seal to the head surface. Any problem running those with the ****** headers?

 

Do it!.....

 

I was told once by a respectable speed shop that if there is any overhang in the exhaust port that it will just burn through.